It is a manually controlled closed circuit rebreather with back mounted split counterlungs, axial flow scrubber, and three independent P02 (partial pressure of oxygen) displays.

Oxygen Control

The unique feature of the oxygen system is the addition of an oxygen metering orifice. This is NOT a constant mass flow device like the ones used in semi closed rebreathers. What it does is add a small flow of oxygen that is normally set at a surface rate of .7 - 1.0 liters per minute. This addition of 02 greatly reduces the amount of time the diver has to spend adding oxygen. It is in no way a controller and does not reduce the need for the diver to constantly monitor the oxygen level in the breathing loop. As the depth increases the oxygen flow rate decreases due to the increasing ambient pressure and at the same time the rate of change of the P02 slows due to the increased gas density. As much as I would like to claim that these two complimentary features are a result of brilliant design engineering they are in fact just basic physics.

All closed circuit rebreathers require the diver to monitor the P02 regardless of how many computers are built into the rebreather. The fact that the KISS rebreather also requires you to push the button on the oxygen add valve once in a while generally hasn't been seen as a major inconvenience. All CCR training courses teach the student how to manually control the PO2 before allowing them to turn on the computer. It isn't difficult to do. In fact many divers with computer controlled rebreathers have elected to disable the computer and operate the rebreather in manual mode at all times. If you are diving in a task loaded situation such as doing photography, video, spearfishing, or defusing explosive mines then a fully automatic computer controlled rebreather may be your best choice.

P02 Displays

The KISS rebreather has three independent P02 displays. Each of these displays is enclosed in it's own housing, with it's own battery, and reads it's own separate sensor. The probability of all three of these displays failing simultaneously is rather remote. Each display can be replaced independently and spares are easily affordable.


The scrubber is a basic axial flow "there and back" design. It holds approximately 2.7Kg of 4-8 Sofnolime. The axial flow design is resistant to "channeling" (allowing the gas to bypass the scrubber bed) but has higher breathing resistance than radial flow designs. Everything is a compromise. It is rated for three hours in cold water. Some people push them to 4-5 hours and some have done some long surface swims as a result. A C02 hit underwater is an unbelievably ugly experience that can easily prove fatal. This is not an area to be cheap, change it often and start every deep dive with a fresh fill of Sofnolime.


The rebreather uses two back mounted counterlungs (split counterlung) that are avaliable in three sizes; 2, 4, and 6 liter capacity. Some combination of these will normally allow a good match between the counterlung volume and the divers lung capacity. This match permits easier control of buoyancy.
Back mounted counterlungs leave the chest area clear and reduce the number of hoses and fittings compared to over the shoulder counterlungs found on other rebreather designs. They are also subject to changes in breathing resistance as the diver changes positions in the water. If you roll on your back you can expect a case of chipmunk cheeks. Nothing is perfect.

DSV (Mouthpiece)

I used to consider a mouthpiece that could be switched between rebreather and open circuit (OC) mode an essential feature on a rebreather. I don't consider it essential anymore but it is still nice to have. Being able to go to open circuit with just a twist of a knob is convenient for many reasons. It can provide an alternate method of adding diluent gas or even an alternative diluent depending on the connection. It is an easy way to purge the rebreather for verifying the sensor readings and it can prevent panic in the case of a malfunction in the rebreather by allowing a fast simple way of getting your next breath. The drawback of the built in bailout mouthpiece is the size and the fact that the OC regulator has to be de tuned to keep it from freeflowing.

ADV (automatic diluent valve)

This is another feature that I initially considered essential but is actually in the "nice to have" category. This valve adds diluent when the loop volume is reduced by either descending or "breathing down" the volume of oxygen in the loop. Suddenly finding yourself unable to get a breath during a rapid descent could be a panic inducing situation but it is obviously something that a diver can get used to since Buddy Inspiration divers do it all the time. The ADV needs to be set up "tight" enough that it doesn't add diluent without the diver being aware of it but it needs to add enough gas so that a reasonable descent rate can be maintained. Any time the ADV triggers you need to check your P02 because you have either descended and compressed the gas in the loop or you have consumed enough oxygen to reduce the P02 significantly which may also have caused you to loose buoyancy and descend.


I recommend using 13 cubic foot (2 liter) tanks. The limiting factor on the rebreather is the 3 hour scrubber. A 13 cubic foot oxygen tank will provide 5 hours of oxygen at a consumption rate of 1 liter per minute. A 13 cubic foot diluent tank will provide enough gas for an experienced rebreather diver to do two hour long dives to 150 feet. If you carry more gas than this, and you should, it should be in the form of emergency bailout open circuit gas in separate tanks. A larger diluent tank is not an adequate bailout gas supply. Carefully analyze the failure paths on your gas supply and don't put all your eggs (gas) in one basket (tank).


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